Saddam Hussein has been formally declared an enemy prisoner of war, but is still resisting pressure to help his American interrogators after three weeks in custody.

The former dictator, captured almost a month ago, is being given all the rights due him under the Geneva conventions on enemy prisoners of war, a Pentagon spokesman said.

According to British officials, the US administrator in Iraq, Paul Bremer, told Tony Blair in Basra last week that Saddam was being treated gently in an effort to coax him into talking, but that he was "not offering information of an operationally useful kind".

"They are taking their time, trying to get him to talk so that he can feel comfortable that he can talk in captivity," a British official reported him saying.

But Mr Blair was told that documents found in a briefcase in the house near where Saddam was found had helped the US forces to track Iraqi insurgents. The results of his capture were "greater than expected", the prime minister was told.

The UN confirmed yesterday it would not oppose Washington's plan to hand power to an unelected Iraqi government.

Rather than direct elections, the US wants "caucuses" of handpicked "notables" in each of the 18 provinces to choose a transitional national assembly, which would then appoint a government.

In the predominantly Sunni town of Baquba at least six people were killed and 39 injured yesterday by a bomb hidden in a bicycle outside a crowded Shia mosque which exploded as worshippers left after Friday prayers.

The attack was almost certainly the work of Sunni extremists, and appears to be the latest sectarian incident between Iraq's two main religious communities. Baquba is a centre of Iraqi resistance. American troops have carried out numerous raids there, arresting dozens of suspected insurgents.

Shia leaders are unhappy with the plan for transferring power in June, which the US worked out with the Iraq governing council.

Calling for direct elections, Grand Ayatollah Ali Sistani, the senior Shia cleric, said this week that the US plan would not "ensure in any way the fair representation of the Iraqi people".

Supporters of direct elections say they could be held on the basis of the existing Iraqi census and the food ration cards which Iraqis had under the old UN oil-for-food programme. US and British officials say there is no time to organise them properly.

Abdel Aziz Hakim, a senior Shia who headed the governing council last month, wrote to Mr Annan 10 days ago offering a compromise whereby the UN would examine the options and judge their feasibility.

The offer was sensitive, since the US has made it clear that it wants to cut the UN out of the Iraq issue until a new government is formed. Its plan for the transfer of sovereignty made no mention of a UN role.

Barely concealing his annoyance shortly after the plan was announced in November, Mr Annan told reporters: "There have been some questions about whether this was an omission or a message.

After lengthy debate at its New York headquarters, he has accepted that the UN can do little, especially as concern for the security of its own staff is still strong.

In a reply to the governing council's current chairman, Adnan Pachachi, Mr Annan wrote this week that it would be too ambitious to expect the UN "to become involved to a significant extent" in Iraq before the end of June.

Privately, UN officials accept Washington's line that early elections would be ill-prepared.

Security has been a serious issue for the UN since a lorry-bomb destroyed its Baghdad headquarters last August, killing Sergio Vieira de Mello, the head of mission, and 21 other people.

It was the most devastating attack in the UN's 58-year existence. All non-Iraqi staff were withdrawn in October and the UN now runs what is left of its Iraq operations from Cyprus and Jordan.

An early task for the new Iraq government will be to make plans for a constitution and elections held on its basis in 2005.

The US seems willing to give the UN a role once the occupation is formally over. "Our position is that we should prepare for a role after June. It's not practical before," a UN official said last night.

Britain is confident that a sovereign Iraqi government would invite US and British troops to remain as part of a multilateral force approved by the UN security council.

"It would leave the US in overall theatre command rather like Afghanistan," a British official said. "The Iraqi government could always abrogate the agreement but they would have to to take the security consequences."